Chilean intelligence being the black hand behind the protestors rising up against a stolen election is pretty far fetched, South American countries haven't meddled to that level in one another since the XIX century, which was more of a diplomatic free for all in much of the world, so you also saw secret treaties, sponsored coups, puppet Governments, and all that.

Maduro had promised to let international observers in, but began withdrawing the invitations a few months ahead of the elections, and the Carter Foundation was one of two to be allowed a restricted "technical" observation.

The US would benefit from international observers these days, frankly, casting doubts over its electoral system has been used to ill effect to its political stability by bad actors.